Ion implantation has become the technology preferred by industry to dope semiconductors with impurities in the large-scale manufacture of integrated circuits. Ion dose and ion energy are the two most important variables used to define an implant step. Ion dose relates to the concentration of implanted ions for a given semiconductor material. Typically, high current implanters (generally greater than 1 milliamp (mA) ion beam current) are used for high dose implants, while medium current implanters (generally capable of up to about 1 mA beam current) are used for lower dose applications.
Ion energy is the dominant parameter used to control junction depth in semiconductor devices. The energy levels of the ions which make up the ion beam determine the degree of depth of the implanted ions. High energy processes such as those used to form retrograde wells in semiconductor devices require implants of up to a few million electron volts (MeV), while shallow junctions may only demand ultra low energy (ULE) levels below one thousand electron volts (1 KeV).
A typical ion implanter comprises three sections or subsystems: (i) an ion source for outputting an ion beam, (ii) a beamline including a mass analysis magnet for mass resolving the ion beam, and (iii) a target chamber which contains the semiconductor wafer or other substrate to be implanted by the ion beam. Ion sources in ion implanters typically generate an ion beam by ionizing within a source chamber a source gas or vapor, a component of which is a desired dopant element, and extracting the ionized source gas in the form of an ion beam.
Internal parts of ion implanters located along the beamline and in the target chamber may become contaminated by the species being implanted during the course of continued operation. Components that are prone to contamination are those that the ion beam impacts during processing. Along the beamline, components which may become contaminated include the strike plate inside the mass analysis magnet, accelerating electrodes, resolving apertures, and plasma flood components. In the target chamber, at least in high current ion implanters, target wafers are positioned on the periphery of an aluminum disk. The disk is both rotated and translated past a stationary ion beam so that the beam implants ions into the entire surface of the wafer. As a result, portions of the disk not covered by a wafer become contaminated with the dopant species.
Because ion implanters are operated using a variety of process recipes, different types of source gases are run in the source to obtain ion beams comprising the desired species of dopant ions. If, however, the target disk (or other beamline component) becomes contaminated by implantation or sputtering of a species during a previous process recipe (e.g., one involving phosphorous), a later process recipe (e.g., one involving arsenic) may be adversely effected by this cross-contamination. For example, phosphorous which has been sputtered onto or implanted into the surface of an aluminum target disk or beamline component may be dislodged by a subsequent arsenic ion beam, resulting in process contamination.
It is known to generate an ion beam comprised of a reactive species, such as fluorine, between successive implant processes to clean internal portions of an ion implanter (see for example, U.S. Pat. No. 5,554,854 to Blake). However, Blake suggests the use of ionized fluorine to effect such cleaning, because the beam must be ionized (positively) to be transported through the implanter. The Blake system does not suggest the use of an atomic neutral reactive species for cleaning the internal components of an ion implanter.
Accordingly, it is an object of the present invention to provide a system and method for cleaning surfaces to remove contaminants therefrom. It is a further object to provide a system and method for cleaning the internal components of an ion implanter using the ion beam to generate reactive neutral atomic radicals of a cleaning gas. It is still a further object of the present invention to provide such a system and method for use in cleaning either silicon-coated or uncoated internal implanter components.